Polyamideimide resins have excellent heat resistance, chemical resistance and solvent resistance, and are therefore widely used as coating agents for various substrates. For example, polyamideimide resins are used as varnishes for enameled wires and as heat-resistant coating materials and the like.
N-methyl-2-pyrrolidone and the like are well known as the solvents typically used for dissolving, diluting and synthesizing these polyamideimides, and because these solvents are capable of imparting excellent solubility characteristics to polyamideimide resins, they have been widely used up until this point (see Patent Document 1).
Further, in recent years, for reasons including environmental preservation, safety and hygiene, economic viability and coating workability, aqueous resin solutions that use water as the solvent medium instead of an organic solvent are attracting considerable attention. A method for converting a polyamideimide resin to a water-soluble form by reacting a basic compound with the residual carboxyl groups at the resin terminals has been reported (Patent Document 2), and is being used in a variety of applications.